Method and system for notifying 1xev-do system of switching from 1xev-do system to 1x system

ABSTRACT

The present invention comprises: a hybrid access terminal, operating in both a  1 × mode for being provided with a low-rate data transmission service from a  1 × system and a  1 ×EV-DO mode for being provided with a high-rate data transmission service from a  1 ×EV-Do system, periodically switching over to the  1 × system while in traffic with the  1 ×EV-DO system, for transmitting a notice signal for advising the switching over a base station transceiver subsystem including  1 ×EV-DO transceiver subsystem for exchanging a packet data with the hybrid access terminal and a  1 × transceiver subsystem for exchanging a voice or data with the hybrid access terminal and a base station controller including a  1 ×EV-DO controller for controlling a packet data transmission service, of the  1 ×EV-DO transceiver subsystem and a  1 × controller for controlling transmission service of the  1 × transceiver subsystem.

FIELD OF THE INVENTION

The present invention relates to a method and a system for notifying a1×EV-DO system of switching from a 1×EV-DO mode to a 1× mode when ahybrid access terminal (HAT) is switched from the 1×EV-DO mode into the1× mode, and more particularly to a method and a system capable ofcreating a signal notifying a 1×EV-DO system of switching from a 1×EV-DOmode to a 1× mode and transmitting the signal to the 1×EV-DO system byloading the signal in a predetermined channel of a reverse link when ahybrid access terminal in traffic with the 1×EV-DO system is switchedinto the 1× mode in order to search the 1× system.

DESCRIPTION OF THE PRIOR ART

Mobile communication systems have been greatly advanced through 1^(st)generation analog-type advanced mobile phone systems (AMPS) and 2^(nd)generation cellular/personal communication service (PCS) systems.Recently, international mobile telecommunication-2000 (IMT-2000) systemshave been developed and are widely used as 3^(rd) generation high-ratedata communication systems.

The 3GPP2 (3^(rd) Generation Partnership Project2), which is acollaborative international standardization group, offers standards of aCDMA IMT-2000 system as IMT-2000 standards in order to providemultimedia mobile communication services. According to the abovestandards, a high rate packet data system called “1×EV(evolution)” basedon an HDR (high data rate) proposed by Qualcom Incorporated, has beendecided upon as an international standard high rate packet data system.A CDMA 2000 1×EV-DO (data optimized or data only) system has beenupgraded from a CDMA 2000 1× system and is designed to transmit onlydata.

In the following description, the CDMA 2000 1× system is simply referredto as “1× system” and the CDMA 2000 1×EV-DO system is simply referred toas “1×EV-DO system” for the convenience of explanation.

The 1× system utilizes both circuit networks and packet networks andprovides high-rate data services with a maximum transmission rate of307.2 Kbps. In contrast, the 1×EV-DO system is dedicated for packet dataand provides high-rate packet data services with a maximum transmissionrate of 2.4 Mbps.

Currently, the 1×EV-DO system has been used together with theconventional 1× system. That is, both of the 1×EV-DO system and theconventional 1× system are installed in one wireless base station or abase station controller even though they are operated separately fromeach other. In other words, a transceiver of the wireless base stationincludes a channel card for the 1×EV-DO system and a channel card forthe 1× system, respectively. In addition, the base station controllerincludes a data processing board for processing packet data transmittedfrom the 1×EV-DO system and a data processing board for processing datatransmitted from the 1× system, respectively.

High-rate data are transmitted to a mobile communication terminal from amobile communication system, such as the wireless base station or thebase station controller, through the 1×EV-DO system. In addition, voicesignals or low-rate data are transmitted to the communication terminalthrough the 1× system.

A hybrid access terminal capable of receiving communication servicestransmitted from the mobile communication system having both 1×EV-DOsystem and 1× system may periodically monitor each of the 1×EV-DO and 1×systems in a predetermined period of time. That is, the hybrid accessterminal periodically and alternately searches the 1×EV-DO and 1×systems in an idle mode thereof and periodically searches the 1× systemwhen the hybrid access terminal is in traffic with the 1×EV-DO system.

Particularly, the hybrid access terminal in traffic with the 1×EV-DOsystem periodically accesses to the 1× system and updates systemresources, such as system messages and access messages, in order torespond to low-data call signals, such as voice call-accepted signalsand short messages, which may be transmitted to the hybrid accessterminal from the 1× system.

However, the hybrid access terminal must stay in the 1× system until thesystem resources have been completely updated whenever the hybrid accessterminal periodically accesses to the 1× system even if the hybridaccess terminal is in traffic with the 1×EV-DO system.

In addition, the 1×EV-DO system may perform a call drop operation if the1×EV-DO system does not receive a signal from the hybrid access terminalwithin a predetermined period of time (for example, 5.12 seconds) whenthe hybrid access terminal is in traffic with the 1×EV-DO system. Thatis, regardless of reasons thereof, if the 1×EV-DO system detects nosignal from the hybrid access terminal within the predetermined periodof time, the 1×EV-DO system performs the call drop operation withrespect to the hybrid access terminal in order to efficiently utilizethe system resources.

However, currently used 1×EV-DO systems have structures which do notprovide a user with reasons for the call drop operation. In other words,the 1×EV-DO system does not provide the user with information allowingthe user to find a precise reason for the call drop operation, eventhough the call drop operation may happen in various situations, such aswhen the hybrid access terminal making a call-connection with the1×EV-DO system is shifted into a wave shadow zone, when a communicationsystem malfunctions, or when the hybrid access terminal is switched intothe 1× system.

SUMMARY OF THE INVNETION

Therefore, the present invention has been made in view of theabove-mentioned problems, and it is an object of the present inventionto provide a method and a system capable of creating a signal notifyinga 1×EV-DO system of switching from a 1×EV-DO mode to a 1× mode andtransmitting the signal to the 1×EV-DO system by loading the signal in apredetermined channel of a reverse link when a hybrid access terminal intraffic with the 1×EV-DO system is switched into the 1× mode in order tosearch the 1× system.

In order to accomplish the above object, according to a first aspect ofthe present invention, there is provided a system for notifying a CDMA2000 1×EV-DO system of switching from a 1×EV-DO mode into a 1× mode whena hybrid access terminal is switched into the 1× mode, the systemcomprising: a hybrid access terminal operated in relation to a 1× systemand the 1×EV-DO system, the hybrid access terminal in traffic with the1×EV-DO system being periodically switched into the 1× mode in order tosearch the 1× system while transmitting a predetermined signal notifyingthe 1×EV-DO system of switching of the hybrid access terminal from the1×EV-DO mode into the 1× mode if the hybrid access terminal is switchedinto the 1× mode; a base station transceiver subsystem including a1×EV-DO access network transceiver for transmitting/receiving packetdata to/from the hybrid access terminal and a 1× transceiver fortransmitting/receiving voice or data to/from the hybrid access terminal;a base station controller including a 1×EV-DO access network controllerfor controlling a packet data transmission service of the 1×EV-DO accessnetwork transceiver and a 1× controller for controlling a transmissionservice of the 1× transceiver; and a packet data serving node (PDSN)connected to the 1×EV-DO access network controller so as totransmit/receive the packet data to/from the 1×EV-DO system.

According to a second aspect of the present invention, there is provideda method for notifying a CDMA 2000 1×EV-DO system of switching from a1×EV-DO mode into a 1× mode when a hybrid access terminal is switchedinto the 1× mode, the method comprising the steps of: (a) sequentiallyinitializing the 1× mode and the 1×EV-DO mode of the hybrid accessterminal such that the hybrid access terminal stays in an idle state;(b) dual monitoring the 1× mode and the 1×EV-DO mode by using the hybridaccess terminal in a state that the hybrid access terminal stays in theidle state; (c) transmitting/receiving packet data by forming aconnection and a session when the hybrid access terminal enters into atraffic state of the 1×EV-DO mode; (d) switching the hybrid accessterminal into the 1× mode after transmitting a predetermined signal tothe 1×EV-DO system when a predetermined monitoring time lapses; and (e)determining that the hybrid access terminal is switched into the 1× modethrough demodulating the predetermined signal received in the 1×EV-DOsystem.

According to a third aspect of the present invention, there is provideda hybrid access terminal capable of preventing a call drop thereof withrespect to a 1×EV-DO system by notifying the 1×EV-DO system of switchingof the hybrid access terminal from a 1×EV-DO mode into a 1× mode, thehybrid access terminal comprising: a timer repeatedly measuring amonitoring time in order to perform dual monitoring between the 1×EV-DOsystem and a 1× system; a searcher module for tracking and convertingfrequency so as to detect the switching of the hybrid access terminalbetween the 1× mode and the 1×EV-DO mode, and receiving an overheadmessage; a finger module for demodulating the overhead message receivedin the searcher module; and a mobile station modem (MSM) chipalternately and periodically searching the 1×EV-DO system and the 1×system, creating a predetermined signal notifying the switching of thehybrid access terminal from the 1×EV-DO mode into the 1× mode when thehybrid access terminal is switched into the 1× mode, and transmittingthe predetermined signal to the 1×EV-DO system through the searchermodule.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages of the presentinvention will become more apparent from the following detaileddescription when taken in conjunction with the accompanying drawings inwhich:

FIG. 1 is a schematic block view showing a system notifying a 1×EV-DOsystem of switching from a 1×EV-DO mode to a 1× mode when a hybridaccess terminal is switched into the 1× mode according to an exemplaryembodiment of the present invention;

FIGS. 2A and 2B are block views showing a channel structure of a forwardlink for transmitting data to a hybrid access terminal through a 1×EV-DOsystem;

FIG. 3 is a block view showing a channel structure of a reverse link fortransmitting data to a 1×EV-DO system from a hybrid access terminal; and

FIG. 4 is a flowchart showing a procedure for notifying a 1×EV-DO systemof switching from the 1×EV-DO system to a 1× system when a hybrid accessterminal is switched into the 1× system according to an exemplaryembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the preferred embodiments of thepresent invention.

In the following description of the present invention, a detaileddescription of known functions and configurations incorporated hereinwill be omitted when it may make the subject matter of the presentinvention rather unclear.

FIG. 1 is a schematic block view showing. a system 100 notifying a1×EV-DO system of switching from the 1×EV-DO system to a 1× system whena hybrid access terminal 110 is switched into the 1× system according toan exemplary embodiment of the present invention.

As shown in FIG. 1, the system 100 of the present invention includesboth 1×EV-DO system and 1× system. That is, the system 100 has the 1×system making communication with a hybrid access terminal 110 andconsisting of a 1× transceiver 122, a 1× controller 132, and a mobileswitching center (MSC) 140 in order to transmit voice and data. Inaddition, the system 100 has the 1×EV-DO system making communicationwith the hybrid access terminal 110 and consisting of a 1×EV-DO accessnetwork transceiver subsystem (ANTS) 124, a 1×EV-DO access networkcontroller (ANC) 134, a packet data serving node (hereinafter, simplyreferred to as PDSN) 150, and an IP (internet protocol) network 160 inorder to transmit data only.

The hybrid access terminal 110 is divided into two parts so that thehybrid access terminal 110 can receive a voice service and a low-ratedata service from the 1× system and receive a high-rate data servicefrom the 1×EV-DO system, separately. The hybrid access terminal 110 isswitched into a 1× mode when the hybrid access terminal 110 is in anidle state in such a manner that the hybrid access terminal 110 can makecommunication with the 1× system. In this state, the hybrid accessterminal 110 is periodically switched into a 1×EV-DO mode in apredetermined period of time so as to check whether or not data arereceived through the 1×EV-DO system and returns to the 1× mode.According to the exemplary embodiment of the present invention, thehybrid access terminal 110 in traffic with the 1×EV-DO system isswitched into the 1× mode (which is called “switch”) and is againswitched into the 1×EV-DO mode (which is called “return’).

The switch and return functions operating between the 1×EV-DO system andthe 1× system are controlled by means of software stored in a mobilestation modem (MSM) chip, which is a kind of a baseband modem chipaccommodated in the hybrid access terminal 110. In addition, the switchand return functions are achieved by tracking frequencies of eachnetwork using a searcher connected to the MSM chip. That is, when thehybrid access terminal 110 is switched from the 1×EV-DO mode into the 1×mode, a searcher module tracks the frequency of the 1× system under thecontrol of the MSM chip. In addition, when the hybrid access terminal110 returns to the 1×EV-DO mode from the 1× mode, the searcher moduletracks the frequency of the 1×EV-DO system.

When the hybrid access terminal 110 receives data from the 1×EV-DOsystem in the 1×EV-DO mode, a great amount of data may be received inthe hybrid access terminal 110 since the hybrid access terminal 110receives high-rate data in the 1×EV-DO mode. Accordingly, in a case of aforward link for transmitting data from an access network (AN) to thehybrid access terminal 110, channels divided through a CDMA (codedivision multiple access) method may transmit data through time slots,which are divided through a TDM (time division multiplexing) method. Incontrast, in a case of a reverse link for transmitting data from thehybrid access terminal 110 to the 1×EV-DO access network transceiversubsystem 124 and the 1×EV-DO access network controller 134, data aretransmitted through a conventional CDMA method for a plurality ofsubscribers.

In addition, the hybrid access terminal 110 receiving data in trafficwith the 1×EV-DO mode is periodically switched into the 1× mode in apredetermined period of time so as to check whether or not signals, suchas voice signals, are received through the 1× system and returns to the1×EV-DO mode.

The 1× transceiver 122 and the 1×EV-DO access network transceiversubsystem 124 form a base station transceiver subsystem (BTS) 120 so asto provide mobile communication services including voice and data to thehybrid access terminal 110 through an air interface. That is, the basestation transceiver subsystem 120 transmits voice or data to the hybridaccess terminal 110 through the 1× transceiver 122 and transmits onlypacket data to the hybrid access terminal 110 through the 1×EV-DO accessnetwork transceiver subsystem 124.

The 1× controller 132 and the 1×EV-DO access network controller 134 forma base station controller (BSC) 130 for controlling an operation of thebase station transceiver subsystem 120. That is, the 1× controller 132for controlling transmission of voice or data sends voice and/or datatransmitted from the 1× transceiver 122 to the mobile switching center140 and the 1×EV-DO access network controller 134 sends data transmittedfrom the 1×EV-DO access network transceiver subsystem 124 to the PDSN150.

The mobile switching center 140 physically connects a plurality of 1×controllers 132 to another mobile switching center or to a publicswitched telephone network (PSTN) 146 so as to provide a communicationaccess route of the 1× system with respect to a communication calltransmitted from the hybrid access terminal 110 by switching thecommunication access route.

In addition, the mobile switching center 140 processes call signals ofsubscribers by obtaining profile information of the hybrid accessterminal 110 from a home location register (hereinafter, simply referredto as “HLR”) 132, which is a database storing information of hybridaccess terminals registered in the mobile switching center 140, and avisitor location register (hereinafter, simply referred to as “VLR”)134, which is a database storing information of hybrid access terminals110 located in a region of the mobile switching center 140. Herein,profile information includes a mobile identification numbers (MIN), anelectrical serial number (ESN), and supplementary services.

The 1×EV-DO system, which is a high-rate packet data system, isconnected to the PDSN 150 based on TCP/IP so as to transmit/receivevarious data in the form of IP packets to/from the IP network 160. Inaddition, the 1×EV-DO system receives packet data from the IP network160 and transmits the packet data to the hybrid access terminal 110through time slots, which are divided through a TDM method. In addition,the 1×EV-DO system receives CDMA data, which are modulated through aCDMA method, from the hybrid access terminal 110, creates packet data byusing the CDMA data, and transmits the packet data to the PDSN 150.

In a case of a forward link, the 1×EV-DO system transmits data withmaximum power thereof without using a power control of a wireless basestation while providing only a hard handoff function. However, in a caseof a reverse link, the power control is carried out in each terminalwhile providing a soft handoff function as well as the hard handofffunction.

In addition, according to the present invention, when the hybrid accessterminal 110 operated in the 1×EV-DO mode in traffic with the 1×EV-DOsystem is switched into the 1× mode, the hybrid access terminal 110notifies the 1×EV-DO system of switching from the 1×EV-DO mode into the1× mode through a data rate control (DRC) channel by using signalshaving DRC cover values (for example, 0, 1, 2 . . . ). Herein, the DRCchannel exists in the reverse link for transmitting signals or data fromthe hybrid access terminal 110 to the 1×EV-DO system, which will bedescribed in detail with reference to FIG. 3.

Accordingly, since the 1×EV-DO system receives the “switch” of thehybrid access terminal 110 into the 1× system from the hybrid accessterminal 110 through the DRC channel, the 1×EV-DO system may recognizethat the hybrid terminal 110 is operated under the 1× mode. Even if thecall drop of the hybrid access terminal 110 occurs after a predeterminedperiod of time lapses, the 1×EV-DO system can recognize that the hybridterminal 110, which is subject to the call drop, operates in the 1×mode. Of course, the DRC cover value representing the switch of thehybrid access terminal 110 into the 1× mode is predetermined between the1×EV-DO system and the hybrid access terminal 110.

FIGS. 2A and 2B are block views showing a channel structure of a forwardlink for transmitting data to the hybrid access terminal 110 through the1×EV-DO system.

As shown in FIG. 2A, the forward link includes a pilot channel, a mediumaccess control (MAC) channel, a control channel, and a traffic channel.The pilot channel is provided to transmit a pilot signal for allowingthe 1×EV-DO system to track the hybrid access terminal 110. The hybridaccess terminal 110 receives at least one pilot signal through the pilotchannel and accesses to a wireless base station, which has transmitted apilot signal having greatest intensity. In addition, the pilot channelis used as a reference for coherent detection of the wireless basestation having the 1×EV-DO system by means of the hybrid access terminal110.

The MAC channel is mainly used for controlling the reverse link andincludes a reverse activity (RA) channel and a reverse power control(RPC) channel. Herein, the RA channel is used for determining atransmission rate of the reverse link. In addition, the RA channel maybe used for requesting the hybrid access terminal 110 to decrease thetransmission rate when channels of the reverse link are saturated. Inaddition, the RPC channel is used for controlling transmission powerwhen the hybrid access terminal 110 transmits signals or data throughthe reverse link.

The control channel is used for transmitting a broadcast message or adirect message for directly controlling a specific hybrid accessterminal from the 1×EV-DO system to the hybrid access terminal 110. Thetraffic channel is used when the 1×EV-DO system transmits only packetdata to the hybrid access terminal 110.

Hereinafter, a time slot structure and a data structure in the forwardlink will be described with reference to FIG. 2B. Firstly, the forwardlink includes 16 time slots per one frame having a time interval about26.67 ms. In addition, each of the time slots includes a first half slothaving 1024 chips and a second half slot having 1024 chips, that is, thetime slot has total 2048 chips. In addition, a time interval of 1.67 msis allotted to each time slot.

In detail, each of the first half slot and second half slot includes 400data slot chips, 64 MAC slot chips, 96 pilot slot chips, 64 MAC slotchips and 400 data slot chips.

FIG. 3 is a block view showing a channel structure of the reverse linkfor transmitting data to the 1×EV-DO system from the hybrid accessterminal 110.

The reverse link shown in FIG. 3 may use a CDMA method in the samemanner as the 1× system and mainly include an access channel and atraffic channel. The access channel has a pilot channel and a datachannel and the traffic channel has a pilot channel, a MAC channel, anAck channel, and a data channel. Herein, the MAC channel is againdivided into a reverse rate indicator (RRI) channel and a data ratecontrol (DRC) channel.

The access channel is used for transmitting an origination signal(connection_request message), and a registration signal (route_updatemessage). The access channel has a low transmission rate of 9.6 kbps forstability of a wireless channel.

Similar to the pilot channel in the forward link shown in FIG. 2A, thepilot channel shown in FIG. 3 is used as a reference for coherentdetection of the wireless base station having the 1×EV-DO system bymeans of the hybrid access terminal 110. The data channel is used fortransmitting data required for the hybrid access terminal 110 to accessto the 1×EV-DO system.

The traffic channel is used when the hybrid access terminal 110transmits packet data to the 1×EV-DO system. The traffic channelprovides various data transmission rates depending on the wirelesscommunication environment.

The pilot channel performs a function identical to the function of thepilot channel, which has been described with reference to the accesschannel. The MAC channel is used for controlling a data transmissionrate of the traffic channel, so the MAC channel continuously existswhile the hybrid access terminal 110 is being connected to the 1×EV-DOsystem. The RRI channel of the MAC channel is used for representinginformation of the data transmission rate of the traffic channel whenthe hybrid access terminal 110 transmits data through the trafficchannel. An RRI value is displayed in the hybrid access terminal 110.

In addition, the DRC channel determines a data rate, which can bedemodulated, depending on the channel environment of the forward linkand notifies the base station of the data rate. That is, the 1×EV-DOaccess network transceiver subsystem 124 transmits packet data to thehybrid access terminal 110 by using time slots of the forward link. Atthis time, a basis for determining the transmission rate of packet datais the DRC cover value transmitted by the hybrid access terminal 110. Inorder to determine the DRC cover value, the hybrid access terminal 110measures a C/I (carrier to interference) value transmitted from the1×EV-DO access network transceiver subsystem 124 and determines the DCRcover value for the maximum transmission rate.

According to the exemplary embodiment of the present invention, the DRCcover values representing the switch of the hybrid access terminal 110into the 1× system are predetermined between the hybrid access terminal110 and the 1×EV-DO system. For instance, if the DRC cover valuerepresenting the switch of the hybrid access terminal 110 from the1×EV-DO mode into the 1× mode is predetermined as “1”, the hybrid accessterminal 110 is switched into the 1× mode after transmitting the DRCvalue “1” into the 1×EV-DO system through the DRC channel. Accordingly,the 1×EV-DO system can recognize the switch of the hybrid accessterminal 110 into the 1× mode by demodulating the DRC cover valuetransmitted from the hybrid access terminal 110. To this end, DRC covervalues representing the switch of the hybrid access terminal 110 intothe 1× mode must be predetermined between the hybrid access terminal 110and the 1×EV-DO system. In addition, the hybrid access terminal 110 andthe 1×EV-DO system must store the DRC cover values therein,respectively.

FIG. 4 is a flowchart showing a procedure for notifying the 1×EV-DOsystem of switching from the 1×EV-DO system to the 1× system when thehybrid access terminal 110 is switched into the 1× mode according to anexemplary embodiment of the present invention.

When the hybrid access terminal 110 is powered on by a user, the hybridaccess terminal 110 receives the pilot signals from the 1× controller132 and the 1× transceiver 122 of the 1× system so that the 1× mode isinitialized and the hybrid access terminal 110 is maintained in an idlestate. In addition, the hybrid access terminal 110 initializes the1×EV-DO mode by using a system parameter message obtained wheninitializing the 1× mode, and the pilot signals transmitted from the1×EV-DO access network controller 134 and the 1×EV-DO access networktransceiver subsystem 124, and then, the hybrid access terminal 110 ismaintained in the idle state (S400).

After initializing the 1× mode and the 1×EV-DO mode, the hybrid accessterminal 110 performs a dual monitoring between the 1× mode and the1×EV-DO mode (S402).

In addition, the hybrid access terminal 110 monitors the 1× system andthe 1×EV-DO system in the idle state. In this state, if data aretransmitted to the hybrid access terminal 110 from the 1×EV-DO accessnetwork transceiver subsystem 124 or the user requests data to the1×EV-DO system by operating key buttons of the hybrid access terminal110, it is checked whether or not the 1×EV-DO mode is activated and thehybrid access terminal 110 is entered into a traffic state forreceiving/transmitting data (S404). In order to allow the hybrid accessterminal 110 to enter into the traffic state, a connection and a sessionmay be formed between the hybrid access terminal 110 and the 1×EV-DOaccess network transceiver subsystem 124 in such a manner that thehybrid access terminal 110 may transmit/receive data to/from the 1×EV-DOaccess network transceiver subsystem 124.

If the hybrid access terminal 110 enters into the traffic state of the1×EV-DO mode in step S404, the hybrid access terminal 110transmits/receives packet data to/from the 1×EV-DO system (S406).

While transmitting/receiving packet data into/from the 1×EV-DO system inthe traffic state, the hybrid access terminal 110 checks whether or nota predetermined time (for example, 5.12 seconds) lapses by using a timeraccommodated in the hybrid access terminal 110 in order to periodicallysearch the 1× system (S408).

If it is determined that the predetermined time lapses in step 408, thehybrid access terminal 110 transmits a signal including the DRC covervalue, which notifies that the hybrid access terminal 110 is switchedinto the 1× system, to the 1×EV-DO system through the DRC channel of thereverse link and is switched into the 1× system (S410).

Accordingly, the 1×EV-DO access network controller 134 may recognize theswitch of the hybrid access terminal 110 into the 1× mode by receivingand demodulating the signal including the DRC cover value transmittedfrom the DRC channel of the reverse link (S412).

According to the present invention, the 1×EV-DO system can check whetheror not the hybrid access terminal 110 in traffic with the 1×EV-DO systemis switched into the 1× mode in real time, so the reason of the calldrop can be instantly found if the call drop of the hybrid accessterminal 110 occurs while the hybrid access terminal 110 is beingswitched into the 1× mode.

While this invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not limited to thedisclosed embodiment and the drawings, but, on the contrary, it isintended to cover various modifications and variations within the spiritand scope of the appended claims.

INDUSTRIAL APPLICATION

As can be seen from the foregoing, different from the conventional1×EV-DO system, which performs the call drop operation with respect tothe hybrid access terminal without recognizing the reason of the calldrop operation, the present invention notifies the 1×EV-DO system ofswitching from the 1×EV-DO mode into the 1× mode when the hybrid accessterminal is switched into the 1× mode, so the reason of the call drop ofthe hybrid access terminal can be instantly found when the call drop ofthe hybrid access terminal occurs while the hybrid access terminal isbeing switched into the 1× mode.

In addition, according to the present invention, the hybrid accessterminal notifies the 1×EV-DO system of switching from the 1×EV-DO modeinto the 1× mode by using the reverse channel in such a manner that the1×EV-DO system can recognize the reason of the call drop of the hybridaccess terminal, so it is not required to additionally use systemresources of the 1×EV-DO system, thereby preventing the 1×EV-DO systemfrom being subject to overload.

1. A system for notifying a CDMA 2000 1×EV-DO system of switching from a1×EV-DO mode into a 1× mode when a hybrid access terminal is switchedinto the 1× mode, the system comprising: the hybrid access terminaloperated in the 1× mode in relation to a 1× system for receiving a voicesignal transmission service or a low-rate data transmission service fromthe 1× system and in the 1×EV-DO mode in relation to the 1×EV-DO systemfor receiving a high-rate data transmission service from the 1×EV-DOsystem, the hybrid access terminal in traffic with the 1×EV-DO systembeing periodically switched into the 1× mode in order to update anoverhead message while transmitting a predetermined signal notifying the1×EV-DO system of switching of the hybrid access terminal from the1×EV-DO mode into the 1× mode; a base station transceiver subsystemincluding a 1×EV-DO access network transceiver fortransmitting/receiving packet data to/from the hybrid access terminaland a 1× transceiver for transmitting/receiving voice or data to/fromthe hybrid access terminal; a base station controller including a1×EV-DO access network controller for controlling a packet datatransmission service of the 1×EV-DO access network transceiver and a 1×controller for controlling a transmission service of the 1× transceiver;and a packet data serving node (PDSN) connected to the 1×EV-DO accessnetwork controller so as to transmit/receive the packet data to/from the1×EV-DO system.
 2. The system as claimed in claim 1, wherein the hybridaccess terminal is switched to the 1× mode in an idle state thereof inorder to make communication with the 1× system, is periodically switchedinto the 1×EV-DO mode in a predetermined period of time so as to checkwhether or not data are received through the 1×EV-DO system, and thenreturns to the 1× mode.
 3. The system as claimed in claim 1, wherein thehybrid access terminal receiving high-rate data from the 1×EV-DO systemin the 1×EV-DO mode is periodically switched into the 1× mode in apredetermined period of time so as to check whether or not signals arereceived through the 1× system, and then returns- to the 1×EV-DO mode.4. The system as claimed in claim 1, wherein a TDMA (time divisionmultiple access) method is utilized in a case of a forward linktransmitting data from the 1×EV-DO system to the hybrid access terminal,and a CDMA (code division multiple access) method is utilized in a caseof a reverse link transmitting data from the hybrid access terminal tothe 1×EV-DO system.
 5. The system as claimed in claim 4, wherein a hardhandoff is carried out in case of the forward link by transmitting datawith maximum power without performing power control, and a soft handoffis carried out in case of the reverse link while performing the powercontrol with respect to each hybrid access terminal.
 6. The system asclaimed in claim 1, wherein the hybrid access terminal is switched fromthe 1×EV-DO mode into the 1× mode by tracking frequency of the 1× systemusing a searcher module under the control of a mobile station modem(MSM) chip.
 7. The system as claimed in claim 4, wherein the forwardlink includes a pilot channel used for transmitting a pilot signalallowing the 1×EV-DO system to track the hybrid access terminal, a MAC(medium access control) channel used for controlling the reverse link, acontrol channel used for transmitting a broadcast message or a directmessage for directly controlling a specific hybrid access terminal fromthe 1×EV-DO system to the hybrid access terminal, and a traffic channelused for transmitting only packet data from the 1×EV-DO system to thehybrid access terminal.
 8. The system as claimed in claim 1, furthercomprising a mobile switching center for providing a communicationaccess route of the 1× system with respect to a communication calltransmitted from the hybrid access terminal by switching thecommunication access route.
 9. A method for notifying a CDMA 20001×EV-DO system of switching from a 1×EV-DO mode into a 1× mode when ahybrid access terminal is switched into the 1× mode, the methodcomprising the steps of: (a) sequentially initializing the 1× mode andthe 1×EV-DO mode of the hybrid access terminal such that the hybridaccess terminal stays in an idle state; (b) performing dual monitoringwith respect to the 1× mode and the 1×EV-DO mode by using the hybridaccess terminal in a state that the hybrid access terminal stays in theidle state; (c) allowing the hybrid access terminal to enter into atraffic state of the 1×EV-DO mode such that a connection and a sessionare formed between the hybrid access terminal and the 1×EV-DO system,thereby enabling the hybrid access terminal to transmit/receive packetdata to/from the 1×EV-DO system; (d) switching the hybrid accessterminal into the 1× mode after transmitting a predetermined signal tothe 1×EV-DO system when a predetermined monitoring time lapses; and (e)demodulating the predetermined signal received in the 1×EV-DO system todetermine the switching of the hybrid access terminal into the 1× mode.10. The method as claimed in claim 9, wherein, in step (a), the hybridaccess terminal initializes the 1×EV-DO mode by using system parametersobtained when initializing the 1× mode.
 11. The method as claimed inclaim 9, wherein, in step (d), the switching operation is carried out bymeans of a searcher module which tracks frequency of the 1× system underthe control of a mobile station modem (MSM) chip.
 12. The method asclaimed in claim 9, wherein, in step (d), the monitoring time is aconnection time of the hybrid access terminal to the 1×EV-DO systemuntil the hybrid access terminal is switched into the 1× mode.
 13. Themethod as claimed in claim 12, wherein the monitoring time is 5.12seconds.
 14. The method as claimed in claim 9, wherein, in step (d), thehybrid access terminal transmits the predetermine signal through a datarate control (DRC) channel of a reverse link.
 15. The method as claimedin claim 14, wherein the predetermine signal includes information abouta DRC cover value, which is determined in advance and notifies that thehybrid access terminal is switched into the 1× mode.
 16. The method asclaimed in claim 9, wherein, in step (e), the 1×EV-DO system performs acall drop operation for the hybrid access terminal when the hybridaccess terminal switched into the 1× mode represents no response to acall signal of the 1×EV-DO system within a predetermined time.
 17. Themethod as claimed in claim 9, wherein, in step (e), the 1×EV-DO systemdetermines that a call drop of the hybrid access terminal occurs due tothe switch of the hybrid access terminal into the 1× mode, if the hybridaccess terminal switched into the 1× mode represents no response to acall signal of the 1×EV-DO system within a predetermined time.
 18. Themethod as claimed in claim 15 or 17, wherein the 1×EV-DO systemdetermines the switch of the hybrid access terminal into the 1× mode bychecking the DRC cover value through demodulating the predeterminedsignal received in the 1×EV-DO system.
 19. The method as claimed inclaim 16 or 17, wherein the predetermined time is defined in a standardof the 1×EV-DO system as 5.12 seconds.
 20. A hybrid access terminalcapable of preventing a call drop thereof with respect to a 1×EV-DOsystem by notifying the 1×EV-DO system of switching of the hybrid accessterminal from a 1×EV-DO mode into a 1× mode, the hybrid access terminalcomprising: a timer repeatedly measuring a monitoring time in order toperform dual monitoring between the 1×EV-DO system and a 1× system; asearcher module for tracking and converting frequency so as to detectthe switching of the hybrid access terminal between the 1× mode and the1×EV-DO mode, and receiving an overhead message; a finger module fordemodulating the overhead message received in the searcher module; and amobile station modem (MSM) chip alternately and periodically searchingthe 1×EV-DO system and the 1× system, creating a predetermined signalnotifying the switching of the hybrid access terminal from the 1×EV-DOmode into the 1× mode when the hybrid access terminal is switched intothe 1× mode, and transmitting the predetermined signal to the 1×EV-DOsystem through the searcher module.
 21. The hybrid access terminal asclaimed in claim 20, wherein the hybrid access terminal searchesfrequencies used in the 1× system or 1×EV-DO system according to apredetermined monitoring period so as to be operated in the 1× mode or1×EV-DO mode.
 22. The hybrid access terminal as claimed in claim 20,wherein the predetermined signal includes a DRC cover value, which ispredetermined between the 1×EV-DO system and the hybrid access terminal,notifying a switch of the hybrid access terminal into the 1× mode. 23.The hybrid access terminal as claimed in claim 20, wherein the hybridaccess terminal transmits the predetermine signal to the 1×EV-DO systemthrough a data rate control (DRC) channel.